This invention relates generally to communication circuitry and, more particularly, to a system and method of embedding an auxiliary communication link in the overhead structure of a primary communication link.
Auxiliary communication links are often necessary for the maintenance and support of a primary communication link. To that end, a second data link must be established in parallel to the primary data link. For example, an auxiliary telephone line for use in maintenance of the telephone system.
In SONET/SDH communications bytes are reserved in the line overhead section of the frame structure. Many telecommunication users have the expertise to easily construct an auxiliary data link based in the SONET/SDH frame structure. However, the fiber optic technician does not always have access to SONET/SDH messages they pass. Alternately, many fiber optic cable technicians establish a separate redundant line for maintenance communications.
Communication protocols, such as SONET and SDH, typically rely on a fixed header structure to align and synchronize the communications frame structure. While it is critical to operate in accordance with known procedures, there are circumstances when the use of a rigid header structure is detrimental to communications. For example, in a high bit error rate environment, a larger number of bits in the header increases the probability that loss of sync and loss of frame errors will be generated.
It would be advantageous if an auxiliary data link could be established in a communications system without using bytes originally intended for the primary data link.
It would be advantageous if the number and the placement of bits used for synchronization of the data frame structure could be made more flexible, or controllable by the system users.
It would be advantageous if the auxiliary data link could be formed from the overhead structure in the primary data link.
It would be advantageous if the allocation of bytes made for the auxiliary data could be made variable to account for dynamic circumstances, so that the number of auxiliary data bytes could be reduced when more bytes are needed for overhead management, and the number of auxiliary data bits could be increased when a critical auxiliary link message needs to be communicated.
It would be advantageous if the relative location of the auxiliary data link in the overhead section of the primary link could be moved for convenience in communications between system repeaters.
It would be advantageous if the number of bits used for synchronization of the frame structure could be made variable. It would be advantageous if the number of header bits checked to acquire a frame could be made larger than the number of header bits checked for loss of synchronization.
Accordingly, a method for generating an auxiliary communication link is provided. The method comprising:
receiving a first stream of information;
organizing the information into a frame structure which includes a selectable group of overhead bits for synchronization of the frame, and a selectable group of overhead bits to communicate an auxiliary message;
selecting the group of synchronization bits to read;
in response to reading the group of synchronization overhead bits, synchronizing the information into the frame structure;
selecting the group of auxiliary message overhead bits; and
in response to reading the auxiliary message group of overhead bits, recovering an auxiliary message.
The synchronization of the received information into the frame structure includes:
organizing the received information into a block with a header section having a plurality of m bits and a data section;
reading the group of synchronization overhead bits from the header section; and
in which the recovery of the auxiliary message includes reading the group of auxiliary message bits in the header section.
The selection of the group of synchronization overhead bits includes selecting between zero to m bits (all the bits in the header section). The part of the header section not used by the synchronization bits is used for the auxiliary data. Further, the selection of the group of auxiliary message overhead bits includes selecting the location of these bits in the header section.
The method further comprising:
providing a new auxiliary message for transmission;
organizing transmit information into the frame structure including a block with a header section and a data section;
writing the new auxiliary message in the header section of the transmit information; and
transmitting the information.
As in the receiving process, the method comprising:
selecting a group of overhead bits for the synchronization of the transmit information, and a group of overhead bits to communicate the new auxiliary message; and
writing both groups of overhead bits into the header section of the transmit information.
In some aspects of the invention the new auxiliary message is simply the original auxiliary being passed through. Although the same number of header bits must be used to pass the auxiliary message, the location of these bits in the header section may be changed between the reception and transmission of the auxiliary message.
An integrated circuit (IC) transmission repeater with auxiliary data link is also provided. The repeater comprises a decoder to receive information including an auxiliary message written in a second group of selectable overhead bits. The decoder reads a first group of selectable overhead bits to synchronize the received information into a frame structure including a block with a data section and a header section. The decoder has inputs to select the first and second group of overhead bits, and an output to provide the auxiliary message recovered from reading the second group of overhead bits.
As described in the method, the header section has a plurality of m bits, although the header may also be one byte, or less. The decoder reads the first and second group of overhead bits from the header section.
In some aspects of the invention a deinterleaver circuit accepts the received information before the decoder circuit. The deinterleaver has n outputs to provide the received information deinterleaved into n parallel data streams. Then, the decoder accepts the n parallel data streams from the deinterleaver circuit. The decoder reads the first group of overhead bits from the n parallel header sections to synchronize the received information, and reads the second group of overhead bits from n parallel header sections to recover the auxiliary message.
The decoder accepts commands to select the number of second group overhead bits for each of the header sections of the n parallel data streams. Further, the decoder accepts commands for the location of the second group of overhead bits in each of the n header sections.
An encoder accepts a new auxiliary message, and organizes transmit information into the above-mentioned frame structure. The encoder supplies the new auxiliary message written in a fourth group of overhead bits of the header section. The encoder also selects a third group of overhead bits for synchronization of the transmit information. The encoder writes the third group of overhead bits in the header section.
In some aspects of the invention the encoder provides n parallel data streams organized in the frame structure including n blocks having header and data sections. The encoder accepts commands to select the number and location of the fourth group overhead bits in each of the n header sections. An interleaver, connected to the plurality of n encoder outputs, interleaves the n parallel data streams to form the transmit information at the interleaver output.